Diode-pumped solid-state laser with an exchangeable pumping module

ABSTRACT

The invention relates to a diode-pumped solid-state laser (DSSL) comprises a pumping light source having a diode stack. The inventive laser also comprises a laser rod and a pumping cavity, whereby the pumping light source accommodated in a separate housing can be exchanged as a pumping module with simple handles. As a result, the pumping light source is protected from electrostatic discharge of the diodes, mechanical stress and from contamination. Given that it is possible to accommodate alternative pumping light sources of varying pumping capacities in the pumping module, the user can exchange the pumping module when the pumping module is worn as well as when additional power is required.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a diode-pumped solid-state laser (DSSL) with apump light source. The light source has a diode stack, with a laser rodand a pump cavity. The center of the emitting face of the diode stackhas a defined position in space relative to the laser rod.

2. Description of the Related Art

Such a DSSL is disclosed by the publication “Compact 170 Wcontinuous-wave diode-pumped Nd:YAG rod laser with a cusp-shapedreflector” by T. Brand (Optic Letters Vol. 20, p. 1776, 01.09.1995).

Because of their significant advantages, DSSLs are taking over to anincreasing extent from lamp-pumped lasers in many fields of application.Through the technological possibility of arranging a multiplicity oflaser diodes in a row (linear diode array) or a plurality of such lineardiode arrays above one another as a stack (diode stack), it is possibleto form pump light sources with an extremely wide range of pump power.Further, DSSLs have high electro-optical efficiency, long life, betterbeam quality because of the smaller heat input into the active element,and such systems can be designed more compactly because of their lowthermal dissipation.

There are, however, a few disadvantages.

The most significant disadvantage results from the differing divergenceof the diode radiation in the direction of the fast axis (perpendicularto the pn junction) and in the direction of the slow axis (parallel tothe pn junction) of the laser diodes. The radiation from the emittingface of a diode stack with a length equal to the linear diode arraylength and a width equal to the stack height is correspondinglydirectional radiation with a divergence angle of about 15° across thewidth (slow axis) and about 50° across the length (fast axis) of theemitting face (pump radiation).

In order to obtain a high input coupling efficiency for the pumpradiation, the latter must be adjusted in terms of its direction andposition with respect to the active element to be pumped, or whereapplicable with respect to input coupling optics which may also be apump cavity. This means, in practical terms, that the pump light sourcemust be arranged in a particular relative position with respect to theactive element or with respect to the coupling optics. This requirementis the main reason why the pump light source in a DSSL is not easilyinterchangeable, as is usual in the case of lamp-pumped solid-statelasers and is regarded as a particular advantage.

A further disadvantage is the electrostatic sensitivity of the diodes,which are straight away irreparably damaged by an electrostaticdischarge. There are also stringent requirements on the accuracy of thetemperature of the cooling water and the cleanliness of the environment.Condensation of water on the diode likewise leads to their more rapiddegradation.

The aforementioned basic requirements, in particular the need to adjustthe defined relative position, make simple interchanging of the pumplight source impossible in the case of most known DSSL arrangements.

Transverse pumping of the active element without coupling optics,because of the pronounced divergence of the pump radiation in thedirection of the fast axis, is only possible with individual lineardiode arrays which are arranged radially distributed close around theactive element. The number of linear diode arrays can be increased if acylindrical lens is arranged as coupling optics in front of each ofthem, for example, in the linear array direction.

In such solutions, the pump light source is correspondingly a sum ofmany separately arranged individual linear diode arrays, each lineardiode array needing to be adjusted on its own with respect to itscoupling optics. Design solutions in which the user can himself carryout interchanging are not possible.

For longitudinal and transverse pumping, it is known to combine theradiation from individual or even a plurality of linear diode arraysusing sometimes very complicated optics, and to shape it, in such a waythat it can be coupled into an optical fiber.

DSSL arrangements with fiber-coupled linear diode arrays are for exampleknown from U.S. Pat. Nos. 5,127,068, 5,436,990 and 5,446,749 . Thesesystems are suitable for having design configurations such that thelinear diode array with the coupling optics and the optical fiber arearranged in a compact pump module which, should need be, can becompletely interchanged. Since, essentially, only the input coupling ofthe radiation from individual, or only a few, linear diode arrays intoan optical fiber is possible, the possibility of scaling the pump poweris very limited. Further, such pump modules are very expensive sincethey also contain complete coupling optics.

The article “Compact 170 W continuous-wave diode-pumped Nd;YAG rod laserwith a cusp-shaped reflector” by T. Brand (Optic Letters Vol. 20, p.1776, 01.09.1995) describes a transversely pumped DSSL in which the pumpradiation is essentially reflected across a pump cavity into a laserrod. Using this pump cavity, as described by way of example in thearticle, it is possible to couple the pump radiation of a diode stackwith a size of 1 cm (linear diode array length)×4.5 cm (stack height)into a laser rod with 4 mm diameter. This extreme stack height permitshitherto unknown scaling of the pump power using a single pump lightsource. In order to pump the laser rod effectively, the center of theemitting face of the diode stack should be arranged opposite the centerof the laser rod and at a distance from the pump cavity such that it ismaximally illuminated but without having a beam-limiting effect on thepump radiation.

The optical principle of coupling the pump-light radiation in through areflecting pump cavity does not place such extremely stringentrequirements on the accuracy of the adjustment of the pump light sourceas are made in the case of the known input coupling by means oftransmissive input coupling optics. Further, such an arrangement isparticularly advantageous because basically no changes need to be madeto the design dimensions of the pump cavity, which may be configured asdiffuse or specularly reflective and in different geometries, as afunction of the desired pump power, which can be varied by means of thestack height.

THE OBJECT AND SUMMARY OF THE INVENTION

The primary object of the invention is to provide an arrangement for atransversally pumped DSSL which makes it possible to interchange thepump light source by simple handling operations and while beingprotected against electrostatic discharge of the diodes, mechanicalstress and contamination. The intention is for this interchanging to bepossible both in the case of wear by replacing with an equivalent pumplight source, and when a different pump power is needed by replacingwith a different pump light source.

According to the invention, this object is achieved for a DSSL with apump light source having a diode stack, with a laser rod and a pumpcavity, the center of the emitting face of the diode stack having adefined position in space relative to the laser rod or to the pumpcavity, in that the pump light source is fitted in a separate casing ina defined position, and thus forms an interchangeable pump module,which, when inserted into the instrument casing of the DSSL, arrangesthe center of the emitting face of the diode stack in the aforementioneddefined spatial position.

The invention will be explained in more detail below with reference toan illustrative embodiment.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a pump module which fits the embodiment according to FIG.3, in a view facing the laser rod,

FIG. 2 shows the pump module represented in FIG. 1, in a view away fromthe laser rod,

FIG. 3 shows an embodiment of a DSSL according to the invention limitedto the representation of the means essential for the description,without a pump module,

FIG. 4 shows the embodiment represented in FIG. 3 with a pump module.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The center piece of the pump module represented in FIG. 1 is formed by apump light source 1 consisting of a diode stack 2 with an emitting face3 and a cooling system 4.

The pump light source 1 is commercially obtainable in this form.According to different pump power, individual embodiments of this pumplight source 1 differ in terms of the height of the diode stack 2, whichis determined by the number of linear diode arrays arranged above oneanother. As a function of the differing diode stack height, the pumpmodules which differ in terms of pump power have a different length 1.The width b of the pump light source 1 is essentially determined by thelinear diode array length and does not generally differ for the pumplight sources 1 from a given manufacturer. In order for the center ofthe emitting face 3 to be in the required relative position with respectto the laser rod 7 or the pump cavity 8 after the pump module has beeninserted into the DSSL arrangement, it must be arranged inside the pumpmodule in a defined position with respect to the interface with the DSSLarrangement, which will be described below. Because of the differinglength of the pump light sources 1 which are alternatively inserted intothe pump module, there is a need for the possibility of displacement inone direction in space, which in the specific illustrative embodiment iscatered for by the alignment screws 11, while there are fixed stops forthe other directions in space. The pump module can also be given adesign configuration so that such a possibility of displacement is alsoavailable in two or even three directions in space, if the intention isalso for pump light sources 1 from different manufacturers withdifferent external dimensions to be alternatively usable.

The casing of the pump module fulfills several functions.

It gives all the modules arranged inside, in particular the pump lightsource 1, mechanical protection on all sides and likewise protects thelatter against contamination and moisture. In the region of the insertedpump light source 1, it has a window in the front wall 12.4 which is atleast as large as the emitting face 3 of the most powerful pump lightsource 1 that may be used. Further, the cover 12.2 of this casingcontains an opening through which the water input and output adaptersprotrude. Also on the cover 12.2, there is a jack for the electricalconnection of the pump module.

The external shape of the pump module and its dimensions are chosen insuch a way that the cover 12.2 and the rear wall 12.3 form, afterinsertion to a given degree into the instrument housing 5 of the DSSL, auniformly closed structure with the latter (FIG. 4). Using the twoscrews 6, the pump module is fixed in this position. The jack as well asthe water input and output are readily accessible.

A relay 13, which short-circuits the pump light source 1 outside theoperating time in order to prevent an electrostatic discharge, isadvantageously fitted inside the casing.

By the insertion of the pump module into the instrument casing 5, theemitting face 3 is brought into the desired relative position withrespect to the laser rod 7 or to the pump cavity 8.

A prerequisite for this is, as described above, that the center of theemitting face 3 is adjusted during assembly of the pump module withrespect to the faces forming the interface with the DSSL arrangement. Inorder to explain this interface, a Cartesian coordinate system with axesx, y, z has been introduced (FIG. 3). The coordinate origin is placed atthe centroid of the laser rod 7 which the instrument casing 5 of theDSSL contains and with respect to which a pump cavity 8 is arranged in adefined way.

The interface between the DSSL arrangement and the pump module isdefined in the three directions of the coordinate system via mechanicalfaces which are present.

A slideway which is present on the bottom face of the instrument casingand consists of two guide rails 9 embodies the interface on the part ofthe DSSL arrangement in the x and y directions, while the edge of thisbottom face in the region between the guide rails 9 is used as a stopand embodies the interface in the z direction.

On the part of the pump module, the interface is formed by sliding faceson mutually opposite side walls 12.5 of the casing, the spacing of whichcoincides with that of the guide rails 9, and sliding faces on theadjoining regions of the bottom 12.1 in the x and y directions, as wellas a stop 12 on the rear wall 12.3 in the z direction.

The insertion of the pump module via a slideway as far as the stop 10 isa particularly simple design solution for arranging the pump module in adefined fixed spatial position in the instrument casing 5 and thereforewith respect to the laser rod 7 or to the pump cavity 8. This mechanicalinterface may also be configured in a different way using the knowledgeof the person skilled in the art. The pump module may, for example, alsobe slid without a guide into a defined end position which is defined bythree correspondingly arranged fixed stops, or the pump module latchesinto the desired end position with a snap-in connection.

What is claimed is:
 1. A diode-pumped solid-state laser (DSSL)comprising: a pump light source having a diode stack, with a laser rodand a pump cavity, the center of the emitting face of the diode stackhaving a defined position in space relative to the laser rod or to thepump cavity; said pump light source, capable of having alternativelydifferent external dimensions, being fitted in a separate instrumentcasing and thus forming an interchangeable pump module; said instrumentcasing of the DSSL having an opening into which the pump module can beinserted and which is closed by slidable insertion of the pump module;mechanical means being provided in the instrument casing of the DSSL andon the casing of the pump module which form a slidable mechanicalinterface for the relative position of the pump module with respect tothe instrument casing of the DSSL; said laser rod or the pump cavityhaving a unique adjusted relative position with respect to themechanical means which the instrument casing contains; and said centerof the emitting face being adjusted in a defined relative position withrespect to the mechanical means which the instrument casing contains. 2.The DSSL according to claim 1, wherein the mechanical means in theinstrument causing are a slideway consisting of two guide rails, and acasing edge running perpendicular thereto, and the mechanical means onthe casing of the pump module are three mutually orthogonal faces on thecasing itself.
 3. The DSSL according to claim 1, wherein two sides ofthe casing of the pump module are matched to the instrument casing insuch a way that they are freely accessible from outside after the pumpmodule has been inserted into the instrument casing, and the pump modulehas all media connections, including water input and output andelectrical connection, needed for operating the pump light source onthese free sides.
 4. The DSSL according to claim 1, wherein the casingof the pump module contains a relay by which the pump light source canbe short-circuited outside the operating time in order to preventelectrostatic discharge.
 5. A diode-pumped solid-state laser (DSSL)comprising: a pump light source having a diode stack, with a laser rodand a pump cavity, the center of the emitting face of the diode stackhaving a defined position in space relative to the laser rod or to thepump cavity; said pump light source, capable of having alternativelydifferent external dimensions, being fitted in a separate instrumentcasing and thus forming an interchangeable pump module; said instrumentcasing of the DSSL having an opening into which the pump module can beinserted and which is closed by insertion of the pump module; mechanicalmeans being provided in the instrument casing of the DSSL and on thecasing of the pump module which form a mechanical interface for therelative position of the pump module with respect to the instrumentcasing of the DSSL; said laser rod or the pump cavity having a uniqueadjusted relative position with respect to the mechanical means whichthe instrument casing contains; and said center of the emitting facebeing adjusted in a defined relative position with respect to themechanical means which the instrument casing contains; wherein themechanical means in the instrument casing are a slideway consisting oftwo guide rails, and a casing edge running perpendicular thereto, andthe mechanical means on the casing of the pump module are three mutuallyorthogonal faces on the casing itself.
 6. The DSSL according to claim 5,wherein two sides of the casing of the pump module are matched to theinstrument casing in such a way that they are freely accessible fromoutside after the pump module has been inserted into the instrumentcasing, and the pump module has all media connections, including waterinput and output and electrical connection, needed for operating thepump light source on these free sides.
 7. The DSSL according to claim 5,wherein the casing of the pump module contains a relay by which the pumplight source can be short-circuited outside the operating time in orderto prevent electrostatic discharge.